Unit 3 Review

Elements and Symbols

  • All matter is composed of elements, of which there are 118 kinds

  • Elements

    • Are pure substances from which all other things are built

    • Cannot be broken down into simpler substances

    • Have been named for planets, mythological figures, colors, minerals, geographic locations, and famous people

  • Chemical symbols

    • One or two letter abbreviations for the names of elements

    • Only the first letter of an element's symbol is capitalized

    • If the symbol has a second letter, it is lowercase so that we know when a different element is indicated

    • If two letter are capitalized, they represent the symbols of two different elements

Elements: pure substances from which all other things are built; cannot be broken down into simple substances

Chemical Symbols: one or two letter abbreviations for the names of Elements

Ex: cobalt has the symbol Co, hydrogen has the symbol H

The Periodic Table

  • Groups =

    •  vertical columns

    • Shows valence electrons

  • Periods =

    • horizontal rows

    • Shows energy levels

  • Group Names:

    • 1A = Alkali Metals (not hydrogen)

      • Soft, shiny, good conductors, low melting points (metals)

      • Very reactive

    • 2A = Alkaline Earth Metals

    •  7A (17) = 17 Halogens

      • Highly reactive and form compounds w/ most elements

    • 8A (18) = Noble Gases

      • Unreactive

  • Metals:

    • Shiny solids; ductile and malleable

    • Good heat and electricity conductors

    • Higher melting points than nonmetals

    • Solid at room temp (except mercury)

  • Nonmetals:

    • Not shiny, ductile or malleable

    • Poor heat and electricity conductors

    • Low density and melting point

  • Metalloids:

    • Have some properties of metals and some of nonmetals

    • Better at conducting heat and electricity than nonmetals but not metals

    • semiconductors

  • The Periodic Table is the arrangement of the 118 elements

  • Group- a vertical column of elements that have similar properties

    • The group number is written at the top of the column going from 1-18

    • The first two groups and last six groups are known as representative elements and are labelled 1A-8A

    • The middle groups are known as transition elements and are labelled by a number followed by the letter B

 

  • Some groups have specific names

  • Alkali metals- Group 1, soft, shiny metals that are very reactive with water and produce a white substance when exposed to oxygen (except for hydrogen)

  • Alkaline earth metals- Group 2, they have the same properties as Alkali metals but are less reactive

  • Halogens- Group 17,  they are very reactive and will form compounds with most elements

  • Noble Gases- Group 18, stable gases that are nonreactive and hardly found in combination with other elements

 

  • Period- a horizontal row of elements labelled 1-7

    • The amount of elements in a period increase the farther down the periodic table you go

    • Lanthanides and actinides are in periods 6 and 7 even though they are typically shown outside of the periodic table

 

  • There is a heavy zigzag line that separates metals and nonmetals (with the exception of hydrogen)

    • Metals are to the left of the line and nonmetals are to the right

  • Metals - most are shiny solids that are ductile and malleable; they are good conductors of heat and electricity and usually melt at high temperatures (all are solid at room temperature except mercury which is liquid)

  • Nonmetals - not especially shiny, ductile, or malleable and are often poor conductors of heat and electricity; typically have low melting points and densities

  • Metalloids - located on the heavy zigzag line with the exception of aluminum and oganesson; elements that exhibit some properties that are typical of the metals and other properties that are characteristic of the nonmetals;

    • semiconductors - can be modified to function as conductors or insulators

Sublevels and Orbitals 

The electrons within the atoms determine the physical and chemical properties of the elements.

 

  • Only a few electrons can occupy the lower energy levels, while more electrons can be accommodated in higher energy levels.

  • The maximum number of electrons allowed in any energy level is calculated using the formula 2n2

Sublevels

  • Each of the energy levels consists of one or more sublevels, in which electrons with identical energy are found.

  • The sublevels are identified by the letters s, p, d, and f.

  • The number of sublevels within an energy level is equal to the principal quantum number, n.

  • For example, the first energy level () has only one sublevel, 1s. The second energy level () has two sublevels, 2s and 2p. The third energy level () has three sublevels, 3s, 3p, and 3d. The fourth energy level () has four sublevels, 4s, 4p, 4d, and 4f.

 

  • Energy levels also have as many sublevels as the value of n, but only s, p, d, and f sublevels are needed to hold the electrons in atoms of the 118 known elements

 

  • Sublevels determine the shape of the electron cloud

  • Within each energy level, the s sublevel has the lowest energy. If there are additional sublevels, the p sublevel has the next lowest energy, then the d sublevel, and finally the f sublevel.

Orbitals

  • The orbital is the three-dimensional volume in which electrons have the highest probability of being found.

  • Each type of orbital has a unique three-dimensional shape. Electrons in an s orbital are most likely found in a region with a spherical shape.

 

  • The orbitals occupied by p, d, and f electrons have three-dimensional shapes different from those of the s electrons.

  • There are three p orbitals.

  • Each p orbital has two lobes like a balloon tied in the middle.

  • The three p orbitals are arranged in three perpendicular directions, along the x, y, and z axes around the nucleus.

  • As with s orbitals, the shape of p orbitals is the same, but the volume increases at higher energy levels.

 

  • Orbitals determine the specific region electrons occupy.

 

Orbitals

  • Orbitals are regions within sublevels where electrons are most likely to be found.

  • Each orbital can hold a maximum of 2 electrons (with opposite spins).

  • Orbitals differ by shape and orientation in space.

Sublevel

Orbital Shape

# of Orbitals

Max Electrons

s

spherical

1

2

p

dumbbell

3

6

d

cloverleaf

5

10

f

complex

7

14

Electrons in Sublevels

  • There is a maximum number of electrons that can occupy each sublevel.

  • An s sublevel holds one or two electrons.

  • Because each p orbital can hold up to two electrons, the three p orbitals in a p sublevel can accommodate six electrons.

  •  A d sublevel with five d orbitals can hold a maximum of 10 electrons. With seven f orbitals, an f sublevel can hold up to 14 electrons.

 Electron Configurations for Period 4 and above:

The 4s sublevel fills before the 3d sublevel. This occurs because the electrons in the 4s sublevel have slightly lower energy than the electrons in the 3d sublevel. This order occurs again in Period 5 when the 5s sublevel fills before the 4d sublevel, in Period 6 when the 6s fills before the 5d, and in Period 7 when the 7s fills before the 6d.

 

At the beginning of Period 4, the electrons in potassium (19) and calcium (20) go into the 4s sublevel. In scandium, the next electron added after the 4s sublevel is filled goes into the 3d block. The 3d block continues to fill until it is complete with 10 electrons at zinc (30). Once the 3d block is complete, the next six electrons, gallium to krypton, go into the 4p block.

Some Exceptions in Sublevel Block Order: When filling the 3d sublevel, exceptions occur for chromium and copper. In Cr and Cu, the 3d sublevel is close to being a half-filled or filled sublevel, which is particularly stable. So the electron configuration for chromium has only one electron in the 4s and five electrons in the 3d sublevel to give the added stability of a half-filled d sublevel.

 Elements have patterns in their properties that repeat across the periodic table.

  • These patterns are called periodic trends

  • Valence electrons: Electrons in the outermost energy level (s & p sublevels).

  • Group number = number of valence electrons (for representative elements).

Atomic Size

  • Definition: Distance from the nucleus to valence electrons.

Trends:

  •  Down a group , atomic size increases
    (electrons added to higher energy levels farther from nucleus)

  • Across a period (L→R)  atomic size decreases
    (more protons , greater pull on electrons)

Ionization Energy (IE)

  • Definition: Energy required to remove one electron from an atom in the gaseous state.

Trends:

  • ↓ Down a group → IE decreases (outer e⁻ farther from nucleus)

  • → Across a period → IE increases (more nuclear charge = stronger attraction)

  • Metals = low IE; Nonmetals = high IE; Noble gases = highest IE

Metallic Character

  • Definition: Tendency of an element to lose valence electrons easily.

  • Metals = igh metallic character

  • Nonmetals = low metallic character

  • Metalloids = intermediate

Trends:

  • ↓ Down a group → metallic character increases

  • → Across a period (L→R) → metallic character decreases

 Valence Electrons: the electrons in the outermost energy level, they occupy the s and p sublevels and can be indicated by the group number

  • Ex: Lithium is in group 1A and has one valence electron

 

Atomic Size: is determined by the distance of the valence electrons from the nucleus, it increases going from top to bottom because the electrons get farther from the nucleus, and decreases from left to right - the elements going across a period, the increase in the number of protons in the nucleus increases the positive charge of the nucleus so, the electrons are pulled closer to the nucleus

 

Ionization Energy: the energy needed to remove one electron from an atom, the attraction of a nucleus for the outermost electrons decreases as the electrons are farther from the nucleus, so the ionization energy decreases going down a group, going across a period from left to right the positive charge of the nucleus increases because there is an increase in the number of protons, so the ionization energy increases going from left to right across the periodic table.

 

Metallic Character: an element that loses valence electrons easily, more prevalent in the elements on the left side of the periodic table, decreases going from left to right across a period, elements in the same group of elements, metallic character increases going from top to bottom - atoms at the bottom of any group have more electron levels, which makes it easier to lose electrons